This invention relates to a knife and surgical procedure where the depth of the incision is precisely limited.
It is known to provide surgical knives with an adjustable guard for limiting the depth of an incision. One such guard is described in the Beaver U.S. Pat. No. 3,945,117 dated Mar. 23, 1976, and comprises a plastic material which resiliently grips the blade. However, such guards are limited by their size and construction to incisions through the skin or other exposed surfaces and the depth of the incision may require great control over the angle at which the knife is held during the procedure, i.e., variation in the angle of the knife to the skin may significantly vary the dept of incision.
In one aspect, it is an object of the present invention to provide a novel knife and surgical method which obviates many of the problems associated with the use of guards on surgical knives, and which may be safely used in confined areas. Accordingly, it is an object of the present invention to provide a novel knife and method of making incisions of precise and easily controllable depth.
However, the present invention finds particular utility in making incisions within the confines of blood vessels, e.g., in the treatment of alterosclerosis by the removal of diseased tissue from an artery. As is well known, endarterectomy is the removal of the intimal and media layers of an artery from the inside of an artery leaving the radially outer adventitia layer intact as the conduit for the blood. A continuing problem with this long used medical procedure is that the withdrawal of the plaque from the artery may result in a xe2x80x9cfeatheredxe2x80x9d endpoint or flap at the point where the removal of tissue stops. Such flaps can limit blood flow and/or be thrombogenic. This possibility is reduced by the termination of the tissue and removal by an incision to provide a clear endpoint, i.e., a termination where all three layers remain attached to each other to thereby prevent blood flow between any two adjacent layers.
As shown in cross-section in FIG. 1, an artery 10 is comprised of three layers, i.e., an outer layer or adventitia 12, a middle or media layer 14, and an intima-tunica or intimal lining 16. Deposits collect on the intimal wall and result in stenosis, blockage or complete obstruction of the flow of blood through the artery. The procedure for removal of a diseased intima and media layer from within the adventitia is known as an endarterectomy, and a new and healthy intima will grow from the adventitia. Devices for performing an endarterectomy are well known and an endarterectomy instrument and method are disclosed in U.S. patent application Ser. No. 09/286,653, entitled xe2x80x9cENDARTERECTOMY LOOPxe2x80x9d, filed Apr. 6, 1999, by the present inventor, the disclosure of which is hereby incorporated herein by reference.
The intima is a thin, several cell thick membrane which is not easily torn but which is readily separated from the media. The media comprises a much thicker layer of muscle cells circular in orientation and the adventitia is the layer which provides the strength of the artery. The media is easily separated from the adventitia and it these two radially inner layers, together with any associated plaque, which it is desirable to remove from the vessel. The media is generally separated from the outer wall by a ring stripper for some axial distance upstream of the endpoint where the media and intima are to be severed. Once the diseased tissue is loosened from the adventia, the diseased tissue may be removed from the vessel.
As shown in FIG. 2, a feathered endpoint may be formed if all three layers do not remain attached to each other. Separation of the layers from each other at the endpoint may result in the formation of a flap 22 between the media 14 and intima 12 or a flap 24 between the adventitia 16 and the media 14 and intima 12. Such a flap 22, 24 in the artery 10 may be flow limiting and/or thrombogenic in nature. FIG. 3 shows a clear endpoint 32 formed in an artery 10 by the use of the present invention.
It is known to address this intima flap problem by vascular stents, but such stents are expensive and reduce the flexibility of the vessel. An alternative is described in the Cox U.S. Pat. No. 5,820,629 dated Oct. 13, 1998, in which a smooth transition in the intimal lining is attempted by an electrocautery coil or a radially extending blade which is inserted down the artery beyond the area of separation of the media, expanded, and then withdrawn to effect cutting of the intima and media. This procedure requires the mechanical operation of the device within the artery and great precision in the angling of the blades and depth of insertion to effect the meeting of the point of separation of the media from the adventitia at the end of the angled cut.
The risk of separation of the three layers is significantly reduced by cutting the media and intima together. It is accordingly an object of the present invention to provide an endarterectomy knife and method which obviates many of the deficiencies of known devices and methods for cutting of the intima and media layers of a blood vessel wall.
It is another object of the present invention to provide a novel device and method in which the blade is shielded from contact with the vessel during insertion and removal thereof and exposed only for the surgical procedure.
It is still another object of the present invention to provide a novel hand held device and method in which the blade is shielded from contact with the vessel during insertion and removal thereof and exposed for the surgical procedure by the angulation of the shaft relative to the vessel or the rotation of the blade relative to the shaft.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.